This study will concern: 1) hypoxic pulmonary vasoconstriction, 2) bronchomotor consequences of cardiac baroreflexes, and, 3) circulatory effects of lung stretch and irritant reflexes. The study of hypoxic vasoconstriction will be done with isolated lungs. It involves a comparison of the vasomotor effects of a number of combinations of alveolar and arterial O tensions, and assumption of a linear PO2 gradient between gas and blood, to define that site in the intervening tissue where hypoxia initiates vasoconstriction. Remaining studies will use open-chest pump-oxygenator perfused dogs in which the systematic arterial pressure can be held constant and lung ventilation can be manipulated without affecting body gas composition. Cardiac barareflex effects on pulmonary compliance and resistance will be appraised by standard methods while individual cardiac chambers are pressurized. The effects of lung and airway distention on systemic vascular resistance, and on selected peripheral beds, will be studied using a similar dog preparation with the heart removed. The effects of both step and cyclic distention will be obtained, and comparisons made between lung and extra-pulmonary airway reflexes. The effects of lung irritants on peripheral resistance and heart rate will be studied using the pump-oxygenator perfused dog. Irritant gases will be passed through the lungs in a constant flow. Comparison will be made between effects of irritants passed through the whole lung with effects when passed only through major airways, and these in turn will be compared with effects of dilute acid or saline instillation into bronchi. In all studies involving reflexes, selective denervation, autonomic blockade and, when relevant, endobronchial anesthesia, will be used to display the reflex nature and explore the major pathways involved.